Conventionally, as this type of body weight support device, for example, Japanese Patent Application Laid-Open No. 2005-169052 discloses a body weight support aid composed of: a saddle on which the user sits in a standing posture; a stick bottom plate for supporting a foot sole; an upper stick integrated with the saddle and fixed to a thigh; a lower stick integrated with the stick bottom plate and fixed to a crus; and a knee flexion coil spring provided between the upper stick and the lower stick. In a swing phase during walking, the body weight support aid supports part of the body weight of the user with his/her knee flexed, by a biasing force of the knee flexion coil spring. The body weight support aid thus aids walking of a walking impaired person having a lower limb disease or the like. This allows the walking impaired person to rotate his/her knee joint and attain a stable gait.